1. Field of Invention
This invention relates to a closure for bottles and, in particular, to a snap-on closure.
2. Brief Statement of the Prior Art
Bottle closures are commonly molded of plastic and are of two types. One type is a twist-on closure or screw closure that engages a threaded neck finish and is applied by threading it on the neck of the bottle. The other type of closure is a snap-on closure which has a peripheral skirt which receives the neck of the bottle and one or more annular beads on its inside wall that snap into receiving grooves of the neck finish of the bottle. Typically, at lease two grooves and beads are provided with a tear tab between the two beads and score lines in the skirt to permit severing of the closure into a reclosure lid and a throw away tear band.
The snap-on closures have frequently been provided with a center corking skirt which is intended to seal the mouth of the bottle. The plastic bottles are blow-molded and the neck finish is achieved with dies commonly referred to as shear steel and neck rings. With frequent or prolonged use, the close tolerances of these dies can be lost with the result that the thicknesses of the neck walls can vary significantly from the original specifications. Furthermore, lack of precise control in manufacturing of the closures frequently results in closures in which the tolerances are not carefully controlled. Difficulties are experienced in the capping operations from both of these causes, and are aggravated by the trend to very light-weight plastic dairy containers, such as the 50-gram gallon container. To illustrate, flashing is trimmed from the neck of the containers during their manufacture and, sometimes, this trimming is imperfect so that necks are obtained which are not perfectly in round or in which the flashing is not completely removed. The result of these fabrication errors is that the container neck frequently wedges between the inner and outer skirts of the closure, lifting the closure or preventing the closure from securely seating.
Consequently, the corking skirt has been designed with minimal dimensions to avoid interference with outsized bottle necks that would prevent the closures from seating on the bottles. This, however, requires that the corking skirt be undersized, and results in loss of the sealing capability of the corking skirt and these closures are notoriously "leakers" in the industry.
Seals of various designs have also been used for the snap-on closures to improve the poor sealing capability of the corking skirt closures. Liners have been ultrasonically and thermally bonded to bottle necks. These seals, however, have only complicated the closure design and increased its manufacturing and application costs.
Manufacturers of press-on closures have also avoided split cavity molds, i.e., molds which split along axially to the plane of the closure, because of their high complexity and cost. Consequently, the tab on the tear band of the closure of one manufacturer is formed on the lower edge of the closure skirts, and a spiral groove is formed starting on the lower edge of the cap skirt and passing upwardly to form a spiral tear band, as in U.S. Pat. No. 3.338,446. Closures of this design, however, are prone to split during the capping operation, since the spiral tear band weakens the bottom edge of the skirt, and caps have a tendency to split along the spiral tear. Other manufacturers have avoided the splitting problem with entirely annular tear bands having lateral tear tabs, however, such closures do not have annular lips on the reclosures, and for this reason are inconvenient to the consumer. Other solutions have provided entirely annular bands, however, these caps leave the lower band of the skirt around the bottle neck after removal of the tear band, and this is also objectionable in some applications.
In my prior patent, U.S. Pat. No. 4,032,029, I disclosed a closure with an annular tear band and tab, and an annular lip. While this closure was a substantial improvement over the aforementioned closures, its manufacture requires a split cavity mold, and it also utilized a less than ideal center corking skirt.